Method for decapsulating package

ABSTRACT

A method for decapsulating a package is provided. The method comprises steps of providing a package having a chip therein, wherein the chip has an active surface and a rear surface. Further, the package further comprises a heat sink, a plurality of solder bumps, a substrate, an underfill and a plurality of solder balls. The method further comprises removing the heat sink and removing the substrate together with the solder balls. A dry etching process is performed to remove a portion of the underfill. A wet etching process is performed to remove the rest portion of the underfill. A thermal process solder bump removal process is performed to melt the solder bumps and then a solder bump removal process is performed to remove the melted solder bumps from the active surface of the chip.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.11/535,073, filed on Sep. 26, 2006, and all benefits of such earlierapplication are hereby claimed for this new continuation application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor process. Moreparticularly, the present invention relates to a technology to detectionof a method for decapsulating a package.

2. Description of the Prior Art

Integrated circuit (IC) packaging is a way of separating the IC chips ona wafer after the front-end semiconductor fabrication process,connecting the chips to individual lead frames and encapsulating thechips for a better protection. At present, the most common chippackaging technique includes the flip chip interconnect technology. Themethod includes providing conductive bumps on the input/output (I/O)contacts of a chip and then flipping over the chip so that the bumps candirectly contact a substrate. The major advantages of the flip chipbonding technique are small area occupation, high lead count, shortinterconnect, low inductance and easy-to-control noise level. As aresult, the flip chip package is particularly suitable for producinghigh-speed, high-performance, light and compact device.

In order to perform a failure analysis on the package or to conduct arework process on the package, it is necessary to decapsulate thepackage to be a chip without having the solder bumps and the underfillthereon. The most common method for removing the underfill and thesolder bumps is to grind or polish away the substrate from the chip andremove the underfill and the solder bumps as well. However, the surfaceof the chip is easily damaged during the grinding or polishing process.Therefore, the electrical probing during the failure inspection isseriously affected by the grinding or polishing result. Furthermore, byusing the grinding or polishing process, the solder bumps are removedtogether with the underfill. Therefore, when the underfill is the onlypart needed to be rework, it is hard to remove the underfill but leavethe solder bumps on the chip by using the grinding or polishing process.

In order to remove the underfill without removing the solder bumps or toremove the solder bumps without damaging the underfill, the industrydevelops several ways. However, none of the methods can remove theunderfill completely without leaving the underfill residual on the chipor can remove the underfill completely without damaging the solderbumps. Furthermore, none of the methods can remove the solder bumpswithout damaging the metal pads on the chip or can remove the solderbumps without spending a lot of money.

SUMMARY OF THE INVENTION

Accordingly, at least one objective of the present invention is toprovide a method for removing an underfill from a chip. By applying themethod according to the present invention, the underfill is completelyremoved without damaging the solder bumps.

At least another objective of the present invention is to provide amethod for removing solder bumps from a chip. By applying the methodaccording to the present invention, the solder bumps are removed withoutdamaging the metal pads on the chip.

The other objective of the present invention is to provide a method fordecapsulating a package without damaging a chip packed therein.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, theinvention provides a method for removing an underfill from a chip. Themethod comprises steps of providing a chip having an active surface,wherein a plurality of solder bumps are disposed on the active surfaceof the chip and an underfill is disposed over the active surface andfilling between the solder bumps. A dry etching process is performed inan inert-gas environment to remove a portion of the underfill. A wetetching process is performed to remove the rest portion of theunderfill.

According to one embodiment of the present invention, the dry etchingprocess includes a reaction ion etching process.

According to one embodiment of the present invention, the inert-gasenvironment includes an argon-gas environment.

According to one embodiment of the present invention, the wet etchingprocess is performed with the use of a fuming nitric acid.

According to one embodiment of the present invention, the wet etchingprocess is performed at a temperature of about 60˜100° C. for about 30seconds˜5 minutes.

According to one embodiment of the present invention, the method furthercomprises a step of performing a purging process to clean the chip byusing nitrogen gas.

The invention also provides a method for removing solder bumps from achip. The method comprises steps of providing a chip having an activesurface, wherein a plurality of solder bumps is disposed on the activesurface. A thermal process is performed to melt the solder bumps andthen a solder bump removal is performed to remove the melted solderbumps from the active surface of the chip.

According to one embodiment of the present invention, the solder bumpremoval process includes a physical stripping-away process.

According to one embodiment of the present invention, the physicalstripping-away process is selected from a group consisting of adisturbing method, a gravity method, suction method, ultrasonic methodand a combination thereof.

According to one embodiment of the present invention, when the thermalprocess is performed at a pressure of about 1 atm, the thermal processis performed at a temperature of about 100˜320° C.

According to one embodiment of the present invention, the thermalprocess is performed in a thermal liquid type system.

According to one embodiment of the present invention, the thermal liquidtype system employs a vacuum oil.

The invention further provides a method for decapsulating a package. Themethod comprises steps of providing a package having a chip therein,wherein the chip has an active surface and a rear surface. Further, thepackage further comprises a heat sink, a plurality of solder bumps, asubstrate, an underfill and a plurality of solder balls. The heat sinkis disposed over the rear surface of the chip. The solder bumps aredisposed on the active surface of the chip. The substrate has a firstsurface connected with the chip through the solder bumps. The underfillis disposed between the chip and the substrate and filling between thesolder bumps. The solder balls are disposed on a second surface of thesubstrate. The method further comprises removing the heat sink andremoving the substrate together with the solder balls. A dry etchingprocess is performed to remove a portion of the underfill. A wet etchingprocess is performed to remove the rest portion of the underfill. Athermal process is performed to melt the solder bumps and then a solderbump removal process is performed to remove the melted solder bumps fromthe active surface of the chip.

According to one embodiment of the present invention, the dry etchingprocess includes a reaction ion etching process.

According to one embodiment of the present invention, the reaction ionetching process is performed in an inert-gas environment.

According to one embodiment of the present invention, the wet etchingprocess is performed with the use of a fuming nitric acid.

According to one embodiment of the present invention, the wet etchingprocess is performed at a temperature of about 60˜100° C. for about 30seconds˜5 minutes.

According to one embodiment of the present invention, the method furthercomprises a step of performing a purging process to clean the chip byusing nitrogen gas before the solder bump removal process is performed.

According to one embodiment of the present invention, the solder bumpremoval process includes a physical stripping-away process.

According to one embodiment of the present invention, the physicalstripping-away process is selected from a group consisting of adisturbing method, a gravity method, suction method, ultrasonic methodand a combination thereof.

According to one embodiment of the present invention, when the thermalprocess is performed at a pressure of about 1 atm, the thermal processis performed at a temperature of about 100˜320° C.

According to one embodiment of the present invention, the thermalprocess is performed in a thermal liquid type system.

According to one embodiment of the present invention, the thermal liquidtype system employs vacuum oil.

In the present invention, by applying the method for removing theunderfill and the method for removing the solder bumps according to thepresent invention in the method for decapsulating the package, theunderfill can be completely removed without damaging the solder bumps orleaving the underfill residual on the chip and the solder bumps can beremoved without damaging the metal pads on the chips. Hence, theperformance of the reverse engineering, the rework process or thefailure inspection process is not affected by the processes for removingthe underfill and the solder bumps. Furthermore, since the solder bumpsare removed by utilizing the physical property of the material of thesolder bumps, the cost for removing the solder bumps is low.

In order to make the aforementioned and other objects, features andadvantages of the present invention comprehensible, a preferredembodiment accompanied with figures is described in detail below.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a package.

FIG. 2 is a process flow showing a method for removing an underfill froma chip according to one embodiment of the present invention.

FIG. 3 is a process flow showing a method for removing solder bumps froma chip according to one embodiment of the present invention.

FIG. 4 is a process flow showing a method for decapsulating a packageaccording to one embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view schematically illustrating a package.FIG. 2 is a process flow showing a method for removing an underfill froma chip according to one embodiment of the present invention. As shown inFIG. 1, a package 1 is provided. The package 1 can be, for example, aflip-chip package. Furthermore, the package 1 comprises a chip 100 and asubstrate 106. The chip 100 further comprises an active surface 100 aand a rear surface 100 b. The chip 100 is disposed over the substrate106 in a way that the active surface 100 a is opposite to the substrate106. There are several solder bumps 102 are disposed on the activesurface of the chip 100 and between the chip 100 and the substrate 106.That is, the substrate 106 is connected to the chip 100 through thesolder bumps 102. Also, an underfill 104 is further disposed between thesubstrate 106 and the chip 100 and filling between the solder bumps 102.Moreover, on the rear surface 100 b of the chip 100, there is a heatsink 110. In addition, there are several solder balls 108 are disposedon a surface of the substrate 106 other than the surface in contact withthe solder bumps 102.

As shown in FIG. 2, before the method for removing the underfill, theheat sink 110 and the substrate 106 with the solder balls 108 areremoved to expose the rear surface 100 b of the chip 100, the underfill104 and the solder bumps 102 (step S201). Then, by following the solidarrows, in the step S202, a dry etching process is performed to remove aportion of the underfill 104 (as shown in FIG. 1). Thereafter, in thestep S204, a wet etching process is performed to remove the rest portionof the underfill 104 to expose a portion of the active surface 100 a ofthe chip 100 and the solder bumps 102. Alternatively, by following thedotted arrows, the underfill 104 can be removed by performing the wetetching process prior to the dry etching process. Then, in the step S206(following either the indication of the solid arrow or the indication ofthe dotted arrow), a purging process is performed to clean the chip 100.Hence, the solder bumps 102 are fully exposed and a portion of theactive surface 100 a of the chip 100 is exposed as well. Therefore, thefailure inspection can be performed on the solder bumps 100 a.

It should be noticed that the dry etching process can be, for example, areaction ion etching process. Also, the dry etching process can be, forexample, performed in an inert-gas environment, such as an argon-gasenvironment. Furthermore, the wet etching process can be, for example,performed with the use of a fuming nitric acid at a temperature of about60˜100° C. for about 30 seconds˜5 minutes. In addition, the purgingprocess can be, for example, performed by spraying the nitrogen gasthrough a nozzle onto the chip.

In the conventional underfill removal process, the underfill is removedby only using the wet etching method so that it takes a lot of the timefor removing the underfill from the chip. Therefore, the time for thesolder bumps exposing under the corrosive solution of the wet etchingprocess is long. Hence, the solder bumps are damaged at the time theunderfill is removed. As for another conventional method for removingthe underfill, the underfill is removed by dry etching only so that aportion of the underfill still remains on the chip. Therefore,inspection accuracy of the failure analysis is affected. By comparing tothe conventional underfill removal process, in the present invention,the wet etching process and the dry etching process are performed toremove the underfill. Therefore, the time for performing the wet etchingprocess is short so that the solder bumps can be prevent from beingdamaged by the etchant. In addition, because of the assistance of thewet etching, the underfill residual left by the dry etching process canbe completely removed.

When the package failure happens on the chip, it is necessary to removethe solder bumps from the chip for further examination. FIG. 3 is aprocess flow showing a method for removing solder bumps from a chipaccording to one embodiment of the present invention. As shown in FIG.3, the chip 100 with the solder bumps 102 is provided (step S301). Itshould be noticed that, the underfill 104 can be either remaining on theactive surface 100 a of the chip 100 or removed beforehand. Then, in thestep S303, a removal process including a thermal process S303 a and asolder bump removal process S303 b is performed to melt the solder bumps102 and then to remove the melted solder bumps from the active surface100 a of the chip 100.

Notably, the solder bump removal process S303 b includes a physicalstripping-away process. Also, the physical stripping-away process can beselected from a group consisting of a disturbing method, a gravitymethod, suction method, ultrasonic method and a combination thereof.Moreover, when the thermal process S303 a is performed at a pressure ofabout 1 atm, the thermal process S303 a is performed at a temperature ofabout 100˜320° C. Furthermore, the thermal process is performed in athermal liquid type system with the use of vacuum oil. That is, duringthe solder bump removal process, the thermal liquid, such as vacuum oil,is used as a heating medium and the solder bumps 102 melt in the thermalliquid and then the melted solder bumps are removed by using a physicaltripping-away process mentioned above. Hence, the metal pads on the chipare exposed.

Taking the commercialized solder bump materials as examples, Table 1shows the compositions and the melting points of three common solderbump materials. According to the material of the solder bumps, theprocess temperature of the solder bump removal process is varied.

TABLE 1 Material Composition Melting points Eutectic Sn/Pb = 63/37 183°C. High lead Sn/Pb = 3/97, 10/90, 5/95 310~320° C. Lead free Major:Sn—Ag and Sn—Ag—Cu 221° C. (Sn/Ag) 217° C. (Sn/Ag/Cu)

In addition, in the conventional method for removing the solder bumpsfrom the chip with the use of a nitric acid-based solution, the solderbumps are eroded by the solution and the metal pads on the chip aredamaged by the solution as well. Furthermore, it is clearly shown in theexperimental data that the removal performance of the nitric acid-basedsolution is poor for removing the solder bumps made of high-leadmaterial. On the contrary, in the method of the present invention, thesolder bumps are removed from the chip by using a method according tothe physical property of the material of the solder bumps. Hence, themetal pads on the chip are not damaged and the cost for performing thesolder bump removal process is low.

FIG. 4 is a process flow showing a method for decapsulating a packageaccording to one embodiment of the present invention. When a reverseengineering, a rework process or a failure inspection process isperformed on the chip, the decapsulation of the package is performed.The method for decapsulating the package is the combination of theaforementioned method for removing the underfill (shown in FIG. 2) andthe method for removing the solder bumps (shown in FIG. 3). As shown inFIG. 4, in the step S401, a package 1 (shown in FIG. 1) is provided.Then, in the step S403, the heat sink 110 is removed and the substrate106 with the solder balls 108 is removed as well. Thereafter, in thestep S405, the underfill 104 is removed. As mentioned above, in themethod for removing the underfill 104, either the dry etching process(S407) or the wet etching process (S409) can be performed first. Thatis, by following the solid arrows, the dry etching process (S409) isperformed prior to the wet etching process (S409). Alternatively, byfollowing the dotted arrows, the wet etching process (S409) is performedprior to the dry etching process (S407). After the underfill 104 isremoved, a purging process is performed by spraying the nitrogen gasonto the chip through a nozzle to clean the surface of the chip 100(S411). Then, the method for removing the solder bumps 102 is performed(S413). As described above, in the step S415, a removal processincluding a thermal process S415 a and a solder bump removal processS415 b is performed to melt the solder bumps 102 and then to remove themelted solder bumps from the active surface 100 a of the chip 100. Therecipes for the method for removing the underfill and the method forremoving the solder bumps are as same as what have mentioned above andare not described herein.

By applying the method for removing the underfill and the method forremoving the solder bumps according to the present invention in themethod for decapsulating the package, the underfill can be completelyremoved without damaging the solder bumps or leaving the underfillresidual on the chip and the solder bumps can be removed withoutdamaging the metal pads on the chips. Hence, the performance of thereverse engineering, the rework process or the failure inspectionprocess is not affected by the processes for removing the underfill andthe solder bumps. Furthermore, since the solder bumps are removed byutilizing the physical property of the material of the solder bumps, thecost for removing the solder bumps is low.

The present invention has been disclosed above in the preferredembodiments, but is not limited to those. It is known to persons skilledin the art that some modifications and innovations may be made withoutdeparting from the spirit and scope of the present invention. Therefore,the scope of the present invention should be defined by the followingclaims.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method for removing an underfill from a chip, comprising: providinga chip having an active surface, wherein a plurality of solder bumps aredisposed on the active surface of the chip and an underfill is disposedover the active surface and filling between the solder bumps; performinga dry etching process in an inert-gas environment to remove a portion ofthe underfill; and performing a wet etching process to remove the restportion of the underfill.
 2. The method of claim 1, wherein the dryetching process includes a reaction ion etching process.
 3. The methodof claim 1, wherein the inert-gas environment includes an argon-gasenvironment.
 4. The method of claim 1, wherein the wet etching processis performed with the use of a fuming nitric acid.
 5. The method ofclaim 1, wherein the wet etching process is performed at a temperatureof about 60˜100° C. for about 30 seconds˜5 minutes.
 6. The method ofclaim 1 further comprising performing a purging process to clean thechip by using nitrogen gas.
 7. A method for removing solder bumps from achip, comprising: providing a chip having an active surface, wherein aplurality of solder bumps are disposed on the active surface; performinga thermal process to melt the solder bumps; and performing a solder bumpremoval process to remove the melted solder bumps from the activesurface of the chip.
 8. The method of claim 7, wherein the solder bumpremoval process includes a physical stripping-away process.
 9. Themethod of claim 8, wherein the physical stripping-away process isselected from a group consisting of a disturbing method, a gravitymethod, suction method, ultrasonic method and a combination thereof. 10.The method of claim 7, wherein, at a pressure of about 1 atm, thethermal process is performed at a temperature of about 100˜320° C. 11.The method of claim 7, wherein the thermal process is performed in athermal liquid type system.
 12. The method of claim 11, wherein thethermal liquid type system employs a vacuum oil.